Rare earth doped oxyhalide laser glass

ABSTRACT

The oxyhalide rare earth doped laser glass of the present invention comprises the substitution of fluorine for oxygen in glasses having the general molar batch composition of 50% SiO 2 , 25% CaO, 25% Al 2  O 3  to improve the distribution of rare earth dopants in the glass. The general molar batch composition of the invention ranges from approximately 45-70% SiO 2 , 15-35% CaO, 10-25% Al 2  O 3 , 4-15% Al 2  F 6 , and 0.001-2% Er 2  O 3 . This substitution of fluorine into the 2SiO 2 . Al 2  O 3 . CaO glass system provides erbium doped laser glasses having a Er 2  O 3  batch content of 0.01 mole % Er 2  O 3  to 1.2 mole % Er 2  O 3  (500 ppm Er 2  O 3  to 5.68 wt. % Er 2  O 3 ) which show little to no concentration quenching and exhibit useful fluorescence lifetimes of approximately 6 milliseconds (ms) or greater.

This application claims the benefit of U.S. provisional application No.60/015,801, filed Apr. 17, 1996.

FIELD OF THE INVENTION

This invention relates to oxyhalide laser glasses doped with rare earthelements.

BACKGROUND OF THE INVENTION

It is known in the prior art that laser glasses may be produced bydoping silica glass with rare earth elements. The laser property of suchrare earth doped laser glasses is derived from the light amplificationachieved by stimulated emission of the excited rare earth element ionsdoped in the glass and is dependent on the fluorescence lifetime of thedoped ions. It is further known that the laser output of a laser glassis dependent on the number of rare earth ions present in the glass.

The problem in the prior art has been that a maximum usableconcentration of rare earth ions in a laser glass is quickly reached dueto the phenomenon of concentration quenching. Concentration quenching isdue to the non-radiative decay of excited rare earth ions which are tooclose to their neighboring unexcited rare earth ions. Excited rare earthions will transfer energy to closely neighboring non-excited rare earthions through dipole-dipole coupling, resulting in no net output oflight. As the concentration of rare earth ions in a laser glass isincreased, the rare earth ions tend to cluster close together withneighboring rare earth ions, consequently an increase in actualexcitable rare earth ions responsible for the laser output is notachieved, and the fluorescence lifetime of the rare earth ions isreduced.

The problem faced by the prior art has been to provide a glasscomposition which may be doped to a relatively high rare earth ionconcentration without ion clustering reducing the fluorescence lifetimeof the rare earth ions.

Presently erbium is a popular rare earth element used in doping laserglasses, since erbium doped laser glasses can effectively amplify the1.55 μm wavelength of light used in optical telecommunication systems.Neodymium is also used as a rare earth dopant in laser glasses.Accordingly, it is the object of the present invention to provide alaser glass that overcomes the problems of the prior art.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a glasscomposition having a relatively high concentration of excitable erbiumions resistant to clustering which can be advantageously used in laserapplications such as planar optical amplifiers and other compact laserproducts which require a high concentration of excitable ions over ashort path length.

Briefly, the present invention relates to an oxyhalide glass compositionwhich allows for an increased rare earth dopant concentration withoutthe detrimental effects of concentration quenching.

In another aspect, the invention relates to an oxyhalide laser glasscomposition which advantageously disperses erbium ions to preventdipole-dipole coupling and provide long fluorescence lifetimes.

In still another aspect, the invention relates to an oxyfluoride aluminasilicate laser glass.

In a further aspect, the invention relates to an oxyfluoride laser glasshaving a fluorine content sufficient to inhibit the detrimental effectsof concentration quenching.

A further objective of the present invention is to disclose a method ofinhibiting concentration quenching of rare earth dopants in an oxideglass.

The inventive composition provides an oxyhalide glass with an increasederbium ion concentration without the detrimental effects ofconcentration quenching. The invention's oxyhalide glass compositionprovides a glass chemistry structure which advantageously disperseserbium ions away from neighboring erbium ions so as to prevent thedipole-dipole coupling of concentration quenching which occurs whenerbium ions are located too close together. The inventive compositionmaximizes total erbium concentration in the glass while also maximizingthe distance between neighboring erbium ions. The inventive compositionallows for relatively high erbium concentrations while providing usefulfluorescence lifetimes.

The inventive oxyfluoride laser glass comprises the substitution offluorine for oxygen in alumina silicate glasses. The distribution oferbium dopant in the glass is improved by replacing a percentage of theAl₂ O₃ in the general molar batch composition of 2SiO₂. Al₂ O₃. CaO withAl₂ F₆. The general molar batch composition of the invention ranges fromapproximately 45-70% SiO₂, 15-35% CaO, 10-25% Al₂ O₃, 4-15% Al₂ F₆, and0.001-2% Er₂ O₃. The inventive batch compositions are melted and formedunder conditions to provide an oxyfluoride glass having at least 6 wt. %F.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of fluorescence lifetime versus Erbium ionconcentration.

FIG. 2 is a plot of fluorescence lifetime versus the analyzed Fluorineweight percent of glasses doped with 0.01 mole percent of Er₂ O₃.

FIG. 3 is a compositional weight percent diagram of the invention.

DESCRIPTION OF THE INVENTION

The inventive oxyhalide glass comprises the substitution of fluorine foroxygen in glasses having the general molar batch composition of 50%SiO₂, 25% CaO, 25% Al₂ O₃ with approximately 11 mole % of the Al₂ O₃batched as Al₂ F₆ to improve the distribution of erbium doped in theglass. The general molar batch composition of the invention ranges fromapproximately 45-70% SiO₂, 15-35% CaO, 10-25% Al₂ O₃, 4-15% Al₂ F₆, and0.001-2% Er₂ O₃. With this substitution of fluorine into the 2SiO₂. Al₂O₃. CaO glass system, the inventor has produced erbium doped laserglasses having a Er₂ O₃ batch content of 0.01 mole % Er₂ O₃ to 1.2 mole% Er₂ O₃ (500 ppm Er₂ O₃ to 5.68 wt. % Er₂ O₃) which show little to noconcentration quenching and exhibit useful fluorescence lifetimes ofapproximately 6 milliseconds (ms) or greater.

The batch compositions of the invention and comparison samples weremelted in covered platinum crucibles for approximately 6 hours atapproximately 1600° C. and then poured onto steel plates to form glassbricks measuring 4"×4"×1/2", which were subsequently annealed at 550° C.Glass testing samples were taken from these glass bricks by scoring andbreaking, and then the fluorescence lifetime of the samples weremeasured in milliseconds (ms) to determine the laser properties of theglass.

Fluorine batch composition ranges of 5 to 11 mole % of Al₂ F₆ (7-15 wt.% F) are particularly preferred for such glass forming conditions.Fluorine retention rates for the melts of the invention vary from 50 to80% depending on the initial fluorine concentration and meltingtemperature. For example, if 30 wt. % F is batched, about 15 wt. % F isactually analyzed in the glass after melting. If 10 wt. % F is batched,about 7 wt. % F is analyzed in the glass after melting. The percentageof F retained in the glass increases with a decreased melt temperature.

The general weight percentage batch compositions of the invention are:

30-45 wt. % SiO₂,

25-45 wt. % Al₂ O₃,

10-25 wt. % CaO,

0.005-10 wt. % Er₂ O₃, and

7-35 wt. % F (batched as Al₂ F₆) with an analyzed fluorine weightpercent after melting of 6.2-20 wt. % F.

The preferred weight percentage batch compositions of the invention are:

37-40 wt. % SiO₂,

30-40 wt. % Al₂ O₃,

15-19 wt. % CaO,

0.005-6 wt. % Er₂ O₃, and

9-30 wt. % F (batched as Al₂ F₆) with an analyzed fluorine weightpercent after melting of 6.5-15 wt. % F.

Table 1 discloses batched weight % compositions of the invention asembodied in samples 1-10. Table 1 also discloses the analyzed weight %of fluorine (F) present in the glass after melting and formation ofsamples 2, 4, 5, 6, 7, 8, 9 and 10.

Table 1 includes the batched weight % compositions of non-fluorinecomparison samples 11, 12, 13, 14, 15, 16, 17, and 19 which weremanufactured and compared to the fluorine containing glasses of theinvention.

                                      TABLE 1                                     __________________________________________________________________________    Weight % Compositions of Samples 1-19                                              1   2   3   4   5   6   7   8   9   10                                   __________________________________________________________________________    SiO.sub.2                                                                          39.4                                                                              39.4                                                                              39.4                                                                              39.4                                                                              39.4                                                                              39.1                                                                              38.7                                                                              38.3                                                                              37.9                                                                              37.2                                 Al.sub.2 O.sub.3                                                                   33.5                                                                              33.5                                                                              33.5                                                                              33.5                                                                              33.5                                                                              33.1                                                                              32.8                                                                              32.5                                                                              32.2                                                                              31.6                                 CaO  18.4                                                                              18.4                                                                              18.4                                                                              18.4                                                                              18.4                                                                              18.2                                                                              18.0                                                                              17.9                                                                              17.7                                                                              17.4                                 Er.sub.2 O.sub.3                                                                   .0050                                                                             .0151                                                                             .0251                                                                             .0377                                                                             .0502                                                                             .995                                                                              1.97                                                                              2.93                                                                              3.86                                                                              5.68                                 F(Batch)                                                                           14.7                                                                              14.6                                                                              14.6                                                                              14.6                                                                              14.6                                                                              14.5                                                                              14.4                                                                              14.2                                                                              14.1                                                                              13.8                                 F(Anal.) 7.1     7.7 10.2                                                                              8.4 8.3 6.7 7.4 7.5                                  __________________________________________________________________________         11  12  13  14   15  16   17  18   19                                    __________________________________________________________________________    SiO.sub.2                                                                          43.1                                                                              43.1                                                                              43.1                                                                              43.1 43.1                                                                              42.7 42.2                                                                              39.7 41.3                                  Al.sub.2 O.sub.3                                                                   36.6                                                                              36.6                                                                              36.6                                                                              36.6 36.6                                                                              36.2 35.8                                                                              33.7 35.1                                  CaO  20.1                                                                              20.1                                                                              20.1                                                                              20.1 20.1                                                                              19.9 19.7                                                                              18.5 19.3                                  Er.sub.2 O.sub.3                                                                   .0055                                                                             .0165                                                                             .0275                                                                             .0412                                                                              .0549                                                                             1.09 2.15                                                                              4.05 4.21                                  F(Batch)                                                                           0   0   0   0    0   0    0   6.7  0                                     F(Anal.)                           4.9                                        __________________________________________________________________________

The fluorescence lifetimes of samples 1-19 were measured by exciting thesamples with an Argon ion laser beam (514 nm). Fluorescent radiationfrom the samples was detected with a Ge photodiode and fluorescentlifetimes were computed therefrom. FIG. 1 presents the fluorescencelifetimes of the erbium ions of samples 1-19 in milliseconds (ms) versusthe erbium dopant density of samples 1-19 in erbium ions per cm³. FIG. 1clearly shows the superior fluorescence lifetime performance of theinvention as compared to the non-fluorine containing samples outlined bythe curve from sample 11 to sample 19. As shown in FIG. 1, as the erbiumweight % is increased from 0.0055 wt. % Er₂ O₃ in sample 11 to 4.21 wt.% Er₂ O₃ in sample 19 (less than 10¹⁸ to greater than 10²⁰ Er ions/cm³),the fluorescence lifetime declines exponentially from 7.5 ms to 3 ms.Over this same range of erbium concentration, the fluorine containingsamples of the invention have markedly improved lifetimes. The inventivecomposition allows for erbium dopant densities greater than 10²⁰ions/cm³ while maintaining useful fluorescence lifetimes of 6 ms andgreater. With the inventive composition, as the erbium concentration isincreased from sample 1 (0.005 wt. % Er₂ O₃ batched) to sample 6 (0.995wt. % Er₂ O₃ batched), the fluorescence lifetime continues to climb. Asthe erbium dopant increases beyond 10²⁰ ion/cm³, the fluorescencelifetime levels off in the 8 to 9 msec range and then declines to 6 msecwith sample 10. The 6 msec lifetime of sample 10 is a utilizable level,especially considering the high erbium concentration. A comparison ofsample 18 (4.05 wt. % Er₂ O₃ batched, 6.7 wt. % F batched, and 4.9 wt. %F analyzed) with samples 8, 9, and 10 discloses that the 4.9 wt. % Fanalyzed in sample 18 is not sufficient to inhibit concentrationquenching at such high erbium densities.

Table 2 and the plot of FIG. 2 show the relationship of fluorine contentanalyzed in the glass after formation to the increased fluorescencelifetimes of the invention and the invention's ability to inhibitconcentration quenching. Table 2 presents the weight % batchcompositions of samples 20-24 along with samples 15 and 5 from Table 1,all of which have a 0.01 mole % Er₂ O₃ batch composition. FIG. 2 clearlyshows the relationship of the fluorine content of the glass to theirfluorescence lifetime.

                                      TABLE 2                                     __________________________________________________________________________    Weight % Compositions Having .01 Mole % Er.sub.2 O.sub.3                      15        20   21  22   5    23  24                                           __________________________________________________________________________    SiO.sub.2                                                                           43.1                                                                              42.0 41.4                                                                              39.7 39.4 36.8                                                                              35.6                                         Al.sub.2 O.sub.3                                                                    36.6                                                                              35.7 35.1                                                                              39.1 33.5 31.3                                                                              30.2                                         CaO   20.1                                                                              19.6 19.3                                                                              15.6 18.4 17.2                                                                              16.6                                         Er.sub.2 O.sub.3                                                                    .0549                                                                             .0535                                                                              .0527                                                                             .0506                                                                              .0502                                                                              .0469                                                                             .0453                                        F(Batch)                                                                            0   4.26 6.98                                                                              9.38 14.6 24.9                                                                              30                                           F(Anal.)  3.61 6.17                                                                              7.04 10.2 12.8                                                                              14.2                                         __________________________________________________________________________

As the analyzed wt. % F of the 0.01 mole % Er₂ O₃ batch compositions areraised from sample 15 which has no F to sample 21 with 6.17 wt. % F thefluorescence lifetime remains stable and in the 6.8-7 ms range. Thenwith an increase of approximately 1 wt. % F, the fluorescence lifetimeof sample 22 jumps up to 8 ms. Increased lifetimes are further achievedwith the increased wt. % F of samples 5, 23, and 24. This threshold wt.% F between 6 and 7% correlates with the fluorine content thresholdbetween sample 18's 4.9 wt. % F and sample 8's 6.7 wt. % F.

The inventive composition inhibits concentration quenching of the erbiumions by providing a glass chemistry structure wherein the erbium ionsare advantageously distributed apart from one another. The fluorinecontent of the inventive composition allows for an increasedconcentration of erbium ion while providing useful fluorescencelifetimes.

As illustrated in the Compositional Weight Percent Diagram of FIG. 3,the general oxide glass composition area 101 of the invention correlateswith the general stoichiometry of the anorthite (CaO.Al2O₃. 2SiO₂) andgehienite (2CaO.Al₂ O₃.SiO₂) crystalline phases, with the addition oferbium and fluorine to provide laser characteristics having adequatefluorescent lifetimes.

The inventor has produced erbium doped oxyfluoride alumina silicateglasses by the substitution of CaO in the batch compositions with ZnO,alkaline and alkaline earth oxides such as MgO, BaO and Na₂ O. Suchglass compositions incorporating the benefits of the invention'sfluorine content to suppress concentration quenching of the rare earthions should exhibit similar laser properties.

The inventive glass compositions further include the substitution of Al₂O₃ in the batch compositions with Ga₂ O₃. Al₂ O₃ can be totallysubstituted in the batch composition with gallium. The inventive glassbatch composition can include from 0-25 mole percent Ga₂ O₃.

The inventive glass compositions further include the substitution ofSiO₂ in the batch compositions with GeO₂. SiO₂ can be totallysubstituted in the batch composition with germanium. The inventive glassbatch composition can include from 0-50 mole percent GeO₂.

The inventive glass composition further includes the substitution of Al₂O₃ in the batch composition with B₂ O₃. Aluminum can be substituted inthe batch composition with boron. The inventive glass batch compositioncan include from 0-15 mole percent B₂ O₃.

In addition to the embodiments discussed above, it will be clear topersons skilled in the art that numerous modifications and changes canbe made to the above invention without departing from its intendedspirit and scope.

I claim:
 1. An erbium doped aluminum silicon calcium oxyfluoride laserglass, said glass having a fluorescence lifetime of at leastapproximately 6 msec, wherein said glass contains 0.005-6 wt. % Er₂ O₃and 6.2-20 wt. % F.
 2. A laser glass as claimed in claim 1, wherein saidglass has a concentration of at least 1×10¹⁷ erbium ions/cm³.
 3. A laserglass as claimed in claim 1, wherein said glass has a concentration ofat least 1×10²⁰ erbium ions/cm³.
 4. A rare earth doped laser glass, saidlaser glass having a molar batch composition comprised of45-70 mole %SiO₂ ; 15-35 mole % CaO; 10-25 mole % Al₂ O₃ ; 4-15 mole % Al₂ F₆ ;0.001-2 mole % Er₂ O₃.
 5. A laser glass as claimed in claim 4, whereinsaid laser glass has a concentration of at least 1×10¹⁷ erbium ions/cm³.6. A laser glass as claimed in claim 4, wherein said glass has aconcentration of at least 1×10²⁰ erbium ions/cm³.
 7. A laser glass asclaimed in claim 4, wherein said glass contains 6.2-20 wt. % F.
 8. Alaser glass as claimed in claim 4, wherein said laser glass exhibits afluorescence lifetime of at least 6 milliseconds.
 9. A laser glasshaving a weight % batch composition comprising:30-45 wt. % SiO₂ ; 25-45wt. % Al₂ O₃ ; 10-25 wt. % CaO; 0.005-10 wt. % Er₂ O₃ ; and 7-35 wt. %F, batched as Al₂ F₆ wherein said glass has an analyzed content of atleast 6.2-20 wt. % F.
 10. A laser glass as claimed in claim 9,whereinwherein said laser glass exhibits a fluorescence lifetime of atleast 6 milliseconds.
 11. A laser glass having a weight % batchcomposition consisting essentially of:37-40 wt. % SiO₂ ; 30-40 wt. % Al₂O₃ ; 15-19 wt. % CaO, 0.005-6 wt. % Er₂ O₃ ; and 9-30 wt. % F, batchedas Al₂ F₆ wherein said glass has an analyzed content of at least 6.5-15wt. % F.
 12. An aluminum silicon oxyhalide laser glass containing adivalent oxide and doped with a plurality of erbium ions, said erbiumions are contained in a concentration of at least 1×10¹⁷ ions/cm³, saidglass having an analyzed fluorine wt. % content of 6.2-20 wt. % fluorinewherein said glass exhibits a fluorescence lifetime of at least 7.6 ms.13. A laser glass as claimed in claim 12, wherein said erbium ions arecontained in a concentration of at least 1×10²⁰ ions/cm³.
 14. An erbiumdoped aluminum silicon oxyfluoride laser glass, which contains adivalent oxide and 0.005-10 wt. % Er₂ O₃ and 6.2-20 wt. % F, whereinsaid glass exhibits a fluorescence lifetime of at least 6 ms.
 15. Alaser glass as claimed in claim 14, wherein said divalent oxide is CaO.16. An optical amplifier formed from an erbium doped oxyfluoiride laserglass having a weight % batch composition comprised of 30-45 wt. % SiO₂,25-45 wt. % Al₂ O₃, 10-25 wt. % CaO, 0.005-10 wt. % Er₂ O₃, wherein saidglass has an analyzed content of 6.2-20 wt. % F.
 17. A method ofinhibiting concentration quenching of a rare earth dopant in a laserglass, said method comprises the steps of providing an erbium silicatelaser glass having a batch composition of MO₂, M¹, M² ₂ O₃ and Er₂ O₃,where M is Si or Ge, M¹ is an oxide of Zn, an alkali metal or analkaline earth metal, and M² is Al, Ga, or B, and substituting an oxygenion in the laser glass with a fluorine ion by replacing a part of anoxide in the batch composition with a fluoride.
 18. A rare earth dopedlaser glass, said laser glass having a molar batch compositionconsisting essentially of:0.001-2 mole % Er₂ O₃ ; 45-70 mole % MO₂ ;15-35 mole % M¹ ; 10-25 mole % M² ₂ O₃ ; 4-15 mole % Al₂ F₆ wherein M isSi or Ge; and M¹ is an oxide of Zn, an alkali metal or an alkaline earthmetal; and M² is Al, Ga, or B.
 19. A rare earth doped laser glass, saidlaser glass having a molar batch composition comprised of:45-70 mole %MO₂ ; 15-35 mole % M¹ ; 10-25 mole % M² ₂ O₃ ; 4-15 mole % Al₂ F₆ ;0.001-2 mole % Er₂ O₃ wherein M is Si or Ge; and M¹ is an oxide of Zn,an alkali metal or an alkaline earth metal; and and M² is Al, Ga; or B.20. A laser glass as claimed in claim 19 wherein the glass contains6.2-20 wt. % F.
 21. A laser glass as claimed in claim 19 wherein saidlaser glass exhibits a fluorescence lifetime of at least 6 milliseconds.22. A method as claimed in claim 17 wherein replacing a part of an oxidein the batch composition with a fluoride comprises replacing Al₂ O₃ withAl₂ F₆.